1. Field of the Invention
The present invention relates to device and method for determining knocking of an internal combustion engine, and particularly to a technique of determining whether knocking is present or absent based on a waveform of vibration of an internal combustion engine.
2. Description of the Background Art
Conventionally, various methods of determining whether knocking (knock) is present or absent have been proposed. For example, by detecting magnitude of vibration occurring in an internal combustion engine and comparing the magnitude with a threshold value, whether knocking is present or absent is determined. However, in an internal combustion engine, besides vibration due to knocking, vibration due to an intake valve or an exhaust valve sitting on its seat may occur. Vibration may also occur due to the actuation of an injector (in particular, an in-cylinder direct injector that directly injects fuel inside a cylinder) or a high-pressure pump that supplies fuel to the injector. When such vibration is detected as noise, it may not be possible to discriminate vibration due to knocking from vibration due to noise, based on magnitude of vibration. Accordingly, a technique of determining whether knocking is present or absent in consideration of both magnitude of vibration and a waveform shape has been proposed.
Japanese Patent Laying-Open No. 2003-021032 discloses a knock control device for an internal combustion engine in which a statistical processing program that determines knocking has occurred when an output value greater than a knock determination value corrected by statistical processing is detected and a waveform shape program determining whether knocking is present or absent from a waveform of vibration are used. The knock control device for an internal combustion engine disclosed in Japanese Patent Laying-Open No. 2003-021032 includes: a knock sensor detecting knocking in an internal combustion engine; a statistical processing portion statistically processing a signal detected by the knock sensor and input through a low-pass filter and a high-pass filter; a first temporal determination portion determining occurrence of knocking based on a processing result by the statistical processing portion; a second temporal determination portion determining occurrence of knocking based on a waveform shape of the signal detected by the knock sensor and input through the low-pass filter and the high-pass filter; and a final determination portion finally determining occurrence of knocking based on the knock temporal determination of the first temporal determination portion and the knock temporal determination of the second temporal determination portion. When both of the first and second temporal determination portions determine that knocking has occurred, the final determination portion finally determines that knocking has occurred.
According to the knock control device disclosed by the publication, a knock temporal determination by a statistical processing program and a knock temporal determination by a waveform shape program are used, and only when both of the temporal determinations determine that knocking has occurred, it is finally determined that knocking has occurred. As a result, occurrence of knocking can precisely be determined even as to an output signal, which has been erroneously determined by a knock determination employing solely the statistical processing program or the waveform shape program.
In the knock control device for an internal combustion engine of Japanese Patent Laying-Open No. 2003-021032, a low-pass filter and a high-pass filter are employed. In order to reduce noise components to improve precision in detecting vibration particular to knocking, it is effective to narrow the bandwidth of a filter extracting only vibration of a predetermined bandwidth. On the other hand, narrowing the bandwidth of a filter, vibration of noise components is removed and, as a result, a characteristic portion of noise components (such as occurrence timing of vibration, attenuation rate and the like) is removed also from the detected waveform. In this case, even as to vibration that is actually due to noise components, a waveform that is similar to a waveform at the time of knocking may be detected. Therefore, the vibration at the time of knocking and the vibration due to noise components are hardly discriminated from each other based on a waveform. However, no consideration on the bandwidth of the filters is made in Japanese Patent Laying-Open No. 2003-021032. Accordingly, even when knocking has not occurred, it may erroneously be determined that knocking has occurred.